Sunday, 2 September 2012

Weasels Digging Holes: American and Honey Badgers

American badger

It was thought at one time that the various species of badger were fairly close relatives within the weasel family. More recent genetic evidence has shown us that that's not the case, and that there is more to their story than one might guess from simply looking at them. While the majority of badgers do indeed belong to a single, related, group - what we might call the "true" badgers - there are some exceptions.

In fact, the badger body plan and lifestyle appear to have evolved at least three times within the weasel family. One instance led to the "true" badgers, with at least four species, and possibly more not yet formally recognised. The other two are no more closely related to the "true" badgers, or even each other, than they are to, say, otters or stoats. In each case, only one member of the lineage survives today, giving us two "subfamilies" with just one living species each.

Of the two, the better known is surely the American badger (Taxidea taxus). Despite being as genetically distant from the European badger as its possible to be without belonging to an entirely different family, it's really not hard to see why early American colonists chose to give it the same name as the animal they were already familiar with. In addition to the short limbs typical of all members of the weasel family, it has a compact, muscular body, wedge-shaped head, and powerful digging claws. That's not really so surprising, when you consider that there are only so many ways to modify the body of a weasel to make it into an effective digger.
What is really striking though, is the fact that they are also a very similar colour and pattern. It's easy enough to tell them apart; the American species has narrower facial stripes that run between the eyes, rather than around them, and it has black cheeks and a white throat, rather than white cheeks and a black throat. But that said, it's still pretty obviously a badger. Quite why both kinds of badger should have independently developed more or less the same coat pattern is a mystery; clearly there's a good reason for it that we just haven't been able to pin down yet.

While there may be only one surviving species of American badger, that species is widespread and numerous. American badgers are found across the central and western USA, with a distinct subspecies around the Great Lakes, as well as much of central Canada and north and central Mexico. Their relatively limited presence in the eastern US is doubtless partly due to the Mississippi being in the way for much of the distance, but it's probably more significant that the badgers prefer the open terrain of plains and scrubland to dense forests. Although they have been hunted to make shaving brushes out of their fur, and there's some inevitable conflict with farmers eliminating their food supply, in general, they're doing well as a species.

One of the key differences between American and European badgers is in their diet. Although European badgers prefer to eat meat when they can, they are essentially omnivores. The American species however, is a pure carnivore. Furthermore, despite being noticeably smaller than the European kind, the animals they do eat are much larger. Rather than preying mainly on earthworms, with only the occasional side order of hedgehogs or mice, the favourite food of American badgers consists of large burrowing rodents, such as gophers, ground squirrels, and marmots.

It is here that their remarkable digging abilities come in, enabling them to rapidly excavate soil to get at the animals beneath. That's not to say that they can't effectively hunt above ground, because they can, and they'll also eat carrion or eggs, and, for that matter, frogs, birds, reptiles or just about anything else than can get their claws on. But it's the digging that really gives them the advantage, and animals like prairie dogs that are their main source of food.

In an unusual display of cross-species cooperation, American badgers have even been observed teaming up with coyotes to get at food. The coyote sniffs out the rodent, and the badger digs it out of the ground for both of them to share. Another tactic they sometimes employ is to block the entrance to a burrow to stop the resident escaping. Generally, this is just with soil that they dig up from the surrounding earth, but they have been seen using various objects lying about in the local landscape - something that qualifies as very basic tool use.

American badgers seem to really dislike one another, and keep well apart outside of the breeding season. Young leave their mother's den at the earliest possible opportunity, and subsequently lead an entirely solitary lifestyle. As a result, the dens of American badgers never reach the complexity and size of the great communal setts of the European species. Nonetheless, they evidently love digging, and while a den consists of no more than a tunnel with a grass-lined chamber at the end, that tunnel can be thirty feet long and extend ten feet below the surface.

Nor are they content with just digging the burrow. An individual badger may have as many as fifty burrows for its exclusive use, and during the summer, uses a different one every day. The end result is mounds of excavated earth across the landscape, which help to maintain the local ecology. The winter, especially in colder climes, is a somewhat different matter. Like European badgers, the American species are nocturnal, but, unlike them, they are capable of entering a state of near-hibernation, and may stay sheltering in a burrow for up to 72 days at a time if the weather is bad enough. Like many hibernating animals, they fatten themselves up through the autumn in preparation for the harsh times ahead, and frequently bury excess animals that they kill so that they can come back to them later.

The breeding season for American badgers is during the summer, but, as with many other members of the weasel family, development of the young is delayed for a few months. Therefore, while it only takes six weeks for the fertilised egg to develop into a newborn badger, the actual pregnancy lasts about seven months, and the young are born in the early spring. Perhaps because the mother can't eat much during the winter, the young are born extremely small - only four ounces compared with a twenty pound plus adult. By the time they are born, however, rodents are plentiful, gorging themselves on new spring growth, and the mother consumes as many as she can to produce produce lots of nutritious milk. This effort means that the badger cubs grow rapidly, and they leave home after only a couple of months. Litters are typically of just two young, although there can be up to six.

Honey badger

The other single-species subfamily among the weasels is that of the honey badger (Mellivora capensis). Also called 'ratels', they are a very successful species, being found across almost the whole of Africa south of the Sahara, as well as in the western portions of that desert, through much of the Middle East, and into Turkmenistan, India, and Nepal. As might be imagined from the sheer size of that range, they are adaptable animals, equally capable of living in tropical forests and deserts, as well as in savannah, steppe, swamps, and mountainous foothills.

Their shape and size are somewhere between those of American and European badgers, but their colour is dramatically different. While some are all-black, most have only black underparts, contrasting sharply with grey to yellow fur above. The two colours are often separated by a clear white line to make them even more obvious. In the wider world, most animals have pale underparts, and it's thought that the reason for that is so that they look uniform when their undersides are in shadow - as they usually will be. That the honey badger is the reverse suggests that it very much wants to be seen, and that's probably as a warning to other animals to stay away.

Honey badgers have a reputation as the most aggressively formidable animals of their size. They have remarkably thick skin, sufficient to resist a dog bite without injury, and apparently impenetrable to snake fangs. Their muscular bodies and powerful digging claws enable them to strike back effectively at anything that annoys them, and they have been reported to inflict significant injuries on animals the size of buffalo. They are also flexible enough to bite somebody holding them by the scruff of the neck, and, in general 'stay away' seems good advice - even if one is inclined to go around pestering wild animals in the first place.

Although they do eat some vegetable matter from time to time, they are primarily carnivorous, and, like American badgers, most of their prey consists of burrowing rodents that they dig out of the ground. But, also like American badgers, they will eat whatever they can catch, including such things as ostrich chicks, domestic sheep, and meerkats. They are strong swimmers, but generally don't hunt that way, although they will stand in streams to swipe fish out of the water, and they are strong enough to crack open turtle shells to get at the meat inside.

As their name indicates, their favourite food appears to be honey - and honey bee grubs. Honey forms only a relatively small proportion of their diet, but they will waste little opportunity to get at it when they can, climbing up into trees and ripping the combs free from the bark. It's often said that that they are alerted to the presence of bee hives by honeyguides, and then share the contents with those birds. Whether this is really true is debatable; while an American badger is surely capable of delivering a powerful swat on the nose to any coyote trying to pinch its food, it's far less likely that a honey badger would even care about a small bird being nearby. Which means that the fact they're often seen together at what is, for both of them, a great source of food, is likely no more than coincidence. Lions and vultures may, in practice, end up sharing the same carcass, but they're hardly cooperating when they do it.

Considering that they have such a reputation for aggression, its worth noting that, in reality, they are far less anti-social than American badgers. True, they are generally solitary animals, but they do not vigorously defend their territories, and seem to tolerate one another's presence. Indeed, there are reports of groups of honey badgers getting together, playing with and scent marking one another for a quarter of an hour or so before going their separate ways. They also scent mark key spots within their territory (and, like many mustelids, have particularly foul-smelling anal scent glands), seemingly for a wide range of purposes, from generally advertising their presence to marking the location of valuable resources.

Honey badgers mate throughout the year, with no particular breeding season. With no delayed implantation, pregnancy lasts a couple of months, and results in the birth of one or two small and hairless cubs. They don't grow anything like as rapidly as American badgers, teething at about a month, and developing the full adult coat of fur at three months. Although they are fully grown by around six months, they don't leave home for at least a year. This pattern is fairly unusual within the weasel family, and suggests that the mother puts a lot more effort into raising her young, at the expense of being able to do so less frequently - a reproductive strategy seen to an even greater extent in humans.